The UCLA Drug Abuse Research Center (DARC) and the Matrix Institute on Addictions, in cooperation with the San Bernardino County California Drug Court (Rancho Cucamonga Division), propose a five-year study to evaluate the effectiveness of using redeemable vouchers to reinforce abstinence and other positive behaviors among participants in a drug court. While research has shown that similar types of contingency management programs can reduce drug use in controlled clinical settings, the use of such interventions within "real world" settings has received little research attention. This approach to reinforcing desirable behavior seems particularly suited to treating substance abusing criminal offenders in drug courts, which tend to place more emphasis on sanctions as punishment for negative behavior. The proposed study will employ a 2x2 design that evaluates two variables: (1) contingent vouchers for drug-free urine samples and (2) contingent vouchers for completion of assigned treatment plan tasks designed to promote abstinence and recovery. Two hundred forty drug court defendants who agree to participate will be randomly assigned to one of four groups (60 participants in each group): (1) standard treatment, no vouchers (standard group); (2) standard treatment plus vouchers contingent upon testing negative for illicit drugs (drug testing group); (3) standard treatment plus vouchers contingent upon completing treatment plan tasks (treatment plan group); and (4) standard treatment plus vouchers contingent upon testing negative for drugs and/or completing treatment plan tasks (combined group). Participation in the intervention will last for the first 6 months of a standard 12-month drug court treatment program that is operated by Matrix Institute. The study will assess the impact of vouchers on program retention, drug use, crime, and other behaviors at completion of the intervention, scheduled completion of the drug court program, and six months following scheduled completion of the drug court; and will address the implementation and cost issues of introducing a contingency management protocol into a typical drug court treatment program. The study has the following specific aims: (1) Determine the impact of vouchers to reinforce abstinence from illicit drugs and completion of treatment plan goals during participation in a drug court treatment program. (2) Determine the impact of vouchers to reinforce abstinence from illicit drugs and completion of treatment plan goals six months after completing the drug court treatment program. (3) Determine if there are client characteristics (e.g., age, gender, primary drug diagnosis, criminal justice history) that are associated with differential treatment outcomes. (4) To provide a qualitative assessment of the impact on court operations and costs of introducing a voucher-based contingency management protocol into a drug court treatment program.